Side and bottom water layer thermal recovery method allowing electrically heating oil deposit in horizontal well

ABSTRACT

Thermal recovery method via electrically heating edge- and bottom-water layer by horizontal wells is presented. Edge- and bottom-water layer is electrically heated by using a plurality of horizontal wells that are located at the upper part of edge- and bottom-water layer, so that the temperature of the whole oil deposit is increased to a state in which in-place oil can flow, by using the theory of centralized heat supply to improve the thermal recovery efficiency. Also disclosed is an electric heating structure for a horizontal well. The electric heating structure is provided with a sieve pipe. A plurality of ferromagnetic permanent magnets is deployed at the upper part of the inner side of the sieve pipe. Spring-shaped electric heating rods serially connected together are disposed in the middle. A heat separation board is disposed in the position of a horizontal diameter. A half lower sieve pipe is sealed and is hollow and jointly separate heat in combination with the heat separation board, and the down transfer of heat energy is reduced.

TECHNICAL FIELD

This method is applicable to heavy oil reservoirs with edge- and bottom-water reservoirs and high pour-point oil reservoirs, which can be recovered thermally in oil industry. This thermal-recovery method is proposed aiming to settle the problems of in-place oil with high viscosity or high paraffin content, low thermal-recovery efficiency of huff and puff or steam flooding, short production plateau, high decline rate and low oil recovery.

TECHNICAL BACKGROUND

Huff and puff, steam flooding, hot-water flooding and in-situ combustion are all efficient technical methods of thermal recovery. However, with gradually in-depth development, more and more problems are exposed during the production. Especially for the middle-deep and super-deep reservoirs (depth 600-2300 m), the contradiction during production is more severe: 1) due to the long-distance transportation, huff and puff, steam flooding, hot-water flooding all have severe thermal loss and low thermal efficiency. There exist high water cut, low production rate, high decline rate in production well and the final reservoir recovery is impacted; 2) although in-situ combustion is effective to production test of some common-heavy oil fault blocks and can satisfy the requirement of industry production, it cannot be applied to most of the super-heavy oil reservoirs, in addition, this development method is destructive and is no less than draining the pond to catch all the fish and killing the goose that lays the golden eggs. Once the reservoir is destroyed, advanced thermal-recovery method in the future will be impossible to conduct. In-situ combustion is one of the worst method; 3) at present, the electrical heating method is confined to pumping rod and borehole heating method. Its purpose is to improve the oil and gas lifting ability of production well, reduce oil viscosity and phenomenon of paraffin precipitation; 4) as for the in-situ thermal-recovery method via electrical heating on oil-shale by hydraulic-fractured horizontal well, it contains great difficulty, high cost, severe pollution to apply it into heavy oil reservoirs; 5) At present, all thermal-recovery methods belong to method of partially heating oil layers. Oil layers are heated unevenly and there exist short thermal effective time, low efficiency and high residual oil saturation, which is mainly located in thermal unswept region and low heat efficiency region.

OPEN TECHNICAL PROBLEMS ABOUT INVENTION Principle Foundation 1. Central Heating

In cold, one gets heat by wearing a coat and one family get heat by firing in the house. As for a building, the best way of getting heat is central heating. The most economic, most effective, most convenient method of the three is central heating. During the process of thermal recovery, huff and puff in single well is similar to one person's getting heat and the composite huff and puff is similar to heating in the house. If the whole reservoir can be regarded as a unit and heated with central heating, the formation temperature can be raised as a whole so that the thermal-recovery problem within single well can be addressed well.

1. “Immersion heater” is a common electrical heater in life and can be used to boil water, heat milk, boil coffee, and so on, which changes the convention that the container is heated from outside of it. By only putting one water-proofed resistance into the container, saving time, saving water, saving electric, saving effort can all be realized, at the same time it is cheap, convenient and effective. For edge- and bottom-water reservoirs, water is natural which makes it possible to electrically heating the water layer. This method is economical, environmentally protective, simple and highly efficient so that it can satisfy the production need well.

3. “Steaming buns with steamer” is one typical example about getting thermal effect by heating with bottom water in daily life. As long as the bottom-water heating continues, the number of steaming layers is not a big deal. The pressure and temperature in the steamer will be released with the remove of steamed buns. When the bottom-water layer of the edge- and bottom-water reservoirs is heated, the temperature will conduct upward to the whole reservoir gradually. The gradually accumulated reservoir pressure (thermal expansion of formation and fluid) and temperature will be released with the oil production effectively. At the same time, the lifting extent of reservoir temperature and pressure can be controlled with heating time and heating temperature, which is convenient. When the whole temperature of the edge- and bottom-water reservoir is in the range of 80° C-100° C., the in-place oil represents the movable state and can be thermally recovered.

4. Gravity Differentiation Phenomenon of Cold and Hot Water Ocean is beamed by the Sun. The water on the top has high temperature and moves downward to the bottom water gradually. The cold water and hot water will represent gravity differentiation except the effect of ocean current. The phenomenon about up-and-down scrolling of cold and hot water will not occur. Heat loss only behaves as the heat conduction between cold and hot water. Therefore, by electrically heating the top of the water layer near the oil layer constantly, the whole temperature of the reservoir can be effectively improved.

Feasibility Demonstration

1. As unite oil and gas systems, edge- and bottom-water reservoirs have the characteristics of fine connection, well close condition of overlying layers, high initial temperature of in-place oil, movable in-place oil, which are the premise of oil and gas migration and accumulation, and in certain temperature range, the phase change of the in-place oil is reversible. The pores where the oil and gas could reach are all effective flow channel and the heat conduction is faster in the formation than in the surrounding mudstone. Heat can conduct gradually from the bottom to the top and be kept effectively be the surrounding mudstone so that the “central heating” can be realized in the whole reservoir.

2. Reservoirs can be categorized into 10 types according to the distribution of oil, gas and water, block bottom-water oil reservoirs, layer-structure block bottom-water oil reservoirs, block edge-,bottom- and top-water oil reservoirs, layer-structure edge-water oil reservoirs, block gas-cap (bottom-water) oil and gas reservoirs, block gas-cap and bottom-water oil and gas reservoirs, layer-structure gas-cap and bottom-water oil and gas reservoirs, layer-structure gas-cap oil and gas reservoirs, pure oil reservoirs, pure gas reservoirs. Except the pure oil reservoirs, pure gas reservoirs and layer-structure gas-cap oil and gas reservoirs, most of the reservoirs develop edge and bottom water and contain adequate formation water resources, which can provide sufficient material guarantee for electrically heating edge- and bottom-water layers by horizontal wells drilled in water layer;

3. Under the condition of geothermal gradient between 2.5° C. and 4.5° C/100 m, the temperature of middle-deep layers and super-deep layers is between 35° C. and 103.5° C. or higher. The temperature difference is 23.5˜47.5° C. for electrically heating the formation water to in-place oil movable condition 80˜150° C. The deeper the formation water layer is, the less electrical energy is needed. The higher the power of electrical heater is, the faster the water temperature rises. On the other side, several electrical heaters could be used simultaneously so that the formation temperature can be improved quickly;

4. For closed oil reservoirs heated as a whole, the characteristics of rising temperature and pressure within the reservoirs is similar to pressure cooker. Under high pressure condition, the boiling pressure of formation water is higher than 100. The relationship between water melting and boiling point and pressure (Table 1) demonstrates that when the formation pressure is 3˜20 MPa, the water boiling pressure is 132.9˜211.4° C. The higher the pressure is, the higher the boiling point is. When the temperature is below the boiling point, the reservoir can be heated to reach the oil movable state. Therefore, keep heating the formation water under high temperature and high pressure. As long as the temperature and pressure test is monitored reasonably in combination with the blow down of production well and pressure release, it is feasible to control the lifting range of formation water temperature and pressure.

5. At present, pipeline skin effect current tracing system, borehole or pumping rod electrical heating system are relative mature. The temperature can be controlled and the material is high temperature resistance, which can satisfy the long distance transportation of electrical energy, so that problems such as heating the production oil, heat dissipation of conductor can be addressed and used well.

6. When “immersion heater” is immersed in the liquid, heat can conduct outside quickly through the liquid so that the liquid can be heated quickly, and the electric wire will not be burned, which is safe, environmentally protective, economic, effective.

7. The technic of electrically heating magnet descaling can settle the scaling problem during electrically heating process effectively. The presence of scale originates from the hard water quality. Magnet can soften the water, which is environmentally protective, economic, convenient and safe. Ferrite magnet, whose components mainly include BaFe12019 and SrFe12019, is made by ceramic technology and bears the characteristics of well temperature resistance, low price, wide application. Ferrite magnet belongs to the permanent magnet;

SOLUTIONS FOR THE PROBLEMS Schemes of Technical Solutions

1) Drill horizontal well in top of the water layer, 20 m away from the oil layer, of the edge- and bottom-water reservoirs and set the electrical heater of horizontal well to electrically heat the water layer.

2) The structure of the electrical heater of horizontal well is shown in FIG. 1. The liner of horizontal-well is divided into upper and lower parts. In the upper part, several spring electrical heaters with series connection are set in the pipe. Heat insulation board is set at the horizontal diameter of the liner. In the lower part, the liner is sealed in vacuum to insulate heat.

3) Several ferrite magnet bars are fixed at the top of the inner liner to prevent scaling.

BENEFICIAL EFFECT OF THE INVENTION Beneficial Effect

Middle-deep-super-deep heavy oil reservoirs and high pour-point oil reservoirs can be recovered safely, environmentally protectively, economically and efficiently so that the development effect can be improved and the final recovery can be promoted.

BRIEF DESCRIPTION TO THE FIGURE Figure Description

1 Slotted liner;

2 Ferrite permanent magnet bar;

3 Spring spiral electrical heater;

4 Heat insulation board;

5 Liner sealing board, inner hollow, prevents the heat transmitting downward in combination with the insulation board.

BEST EXAMPLE ABOUT APPLYING THE INVENTION Best Application Method about the Invention

1) Drill horizontal well in top of the water layer, 20 m away from the oil layer, of the edge- and bottom-water reservoirs, which can store enough thermal energy to raise the temperature of the whole oil layer and delay the formation failure due to premature boiling of the formation water and overpressure.

2) The number, length and trend of horizontal well are determined by size of water body and reservoir volume. Gravel packed open hole completion.

3) If the horizontal production well is used to sidetrack drilling, the conducting wire can be used as borehole or pumping rod electrical heater so that the effect of cooling and heating can be realized; if the horizontal well is drilled individually, the conducting wire needs to use the skin-heat tracing device. High temperature resistant materials should be optimized to prevent the overheated conducting wire in the borehole.

APPLICATION EXAMPLE OF THE INVENTION Application Method of the Invention

Drill several horizontal wells in top of the water layer, near oil layer, of the edge- and bottom-water reservoirs and put the electrical heater into the horizontal well to heat the edge- and bottom-water layers of the oil reservoir so that the temperature of the whole reservoir can be promoted. Use the heat transmitting effect, gas driving effect by overflow of the dissolved gas from water, the thermal expansion pressure of formation water and oil layer as well as the viscosity-reduction effect/wax-precipitation effect of in-place oil under high temperature to recover oil efficiently.

INDUSTRIAL APPLICABILITY

It can be applied to thermally recover heavy oil reservoirs and high pour-point edge- and bottom-water reservoirs, especially for the difficultly recovered heavy oil reservoirs, high pour-point edge- and bottom-water reservoirs at middle or super depth. 

1. One thermal recovery method via electrically heating edge- and bottom-water layers, and the electrical heaters are settled in the horizontal wells so that the water layers could be electrically evenly heated until the temperature of the whole reservoir rises up to what needed for in-place oil to flow, the in-place oil could be thermally recovered; which is different from the method of partially heating oil layer at present.
 2. The structure design characteristic of electrical heater of the horizontal well is that several ferrite permanent magnet bars are fixed at the top of the inner liner and the spring electrical heating bars with series connection are set in the middle part; heat insulation board is set at the horizontal diameter of the liner; the lower liner, in cooperation with heat insulation board to insulate heat, is sealed in vacuum to reduce the downward transmission of thermal energy.
 3. According to the thermal recovery method via electrically heating edge- and bottom-water layers by horizontal wells, which is stated in claim 1, its characteristic is that the Principle Foundation 1 belongs to the central heating and the temperature of the whole reservoir could be risen by heating the edge- and bottom-water layers, which is different from the conventional thermal recovery method by partially heating the oil layer within single well.
 4. According to the thermal recovery method via electrically heating edge- and bottom-water layers by horizontal wells, which is stated in claim 1, its characteristic is that the Principle Foundation 2 points out that the oil, gas and water layers can be regarded as a sealed temperature and pressure system, like the pressure cooker; the temperature and pressure of inner reservoir can be improved quickly to the flow state of the in-place oil by electrically heating the edge- and bottom-water layers of the oil reservoirs.
 5. According to the thermal recovery method via electrically heating edge- and bottom-water layers by horizontal wells, which is stated in claim 1, its characteristic is that the Principle Foundation 3 is the “immersion heater” electric kettle heating method; heating the edge- and bottom-water layer of oil reservoirs through water-proof electrical heater so that the whole oil reservoir can be heated with saving time, saving electricity, saving of fort, cheap, convenience, safety, environmental protection and high efficiency.
 6. According to the thermal recovery method via electrically heating edge- and bottom-water layers by horizontal wells, which is stated in claim 1, its characteristic is that the Principle Foundation 4 is “steaming buns with steamer”; controlling the lifting range of reservoir temperature and pressure by confining the electrical heating time, temperature and recovery methods and save energy by controlling the position of horizontal well in the water layer.
 7. According to the thermal recovery method via electrically heating edge- and bottom-water layers by horizontal wells, which is stated in claim 1, its characteristic is that the Principle Foundation 5 is gravity differentiation phenomenon of cold and hot water; heat loss of electrically heating edge- and bottom-water layers only behaves as the heat conduction between upper hot water and lower cold water; most of the thermal energy moves upward; keeping eletrically heating the edge- and bottom-water layers can improve the temperature of the whole reservoir effectively.
 8. According to the thermal recovery method via electrically heating edge- and bottom-water layers by horizontal wells, which is stated in claim 1, its characteristic is that the Principle Foundation 6 points out that most oft he oil and gas reservoirs develope edge- and bottom-water layers and contain sufficient formation water resources, which can provide enough material guarantee for electrically heating edge- and bottom-water layers by horizontal wells, and at the sametime, provide good refrigerant for electrical heater.
 9. According to the thermal recovery method via electrically heating edge- and bottom-water layers by horizontal wells, which is stated in claim 1, its characteristic is that the Principle Foundation 7 is the representation of geothermal gradient; the deeper the formation water layer buries, the higher the geothermal temperature is and the less electrical energy is needed and the more energy-saving the thermal recovery method via electrically heating edge- and bottom-water layers is.
 10. According to the thermal recovery method via electrically heating edge-and bottom-water layers by horizontal well s, which is stated in claim 1, its characteristic is that the Principle Foundation 8 points out that according to the relationship between formation water temperature and pressure, the formation pressure is 3˜20 MPa and the water boiling point is 132.9˜211.4° C. The higher the pressure is, the higher the boiling point is; when the temperature is below the boiling point, the reservoir can be heated to reach the oil movable state (condition for in-place oil to flow 80˜150° C.).
 11. According to the thermal recovery method via electrically heating edge- and bottom-water layers by horizontal well s, which is stated in claim 1, its characteristic is that the Principle Foundation 9 points out that at present the long distance transportation material is relatively mature and the technic of electrically heating magnet descaling can settle the scaling problem during electrically heating process effectively and keep the heating effect of electrical heater in good state, which can satisfy the requirements of electrically heating edge- and bottom-water layers by horizontal wells in deep and super-deep layers.
 12. According to the thermal recovery method via electrically heating edge- and bottom-water layers by horizontal well s, which is stated in claim 1, its characteristic is that the Principle Foundation 10 uses the viscosity-reduction effect/wax-precipitation effect of in-place oil, the expansion pressure of formation, gas driving effect by overflow of the dissolved gas from water to recover oil. 